A method was developed for measuring low levels of total nitrofurans in animal tissues and milk. The antimicrobial nitrofurans (5 or more products) used in agriculture are extracted from tissue with aqueous acid in the presence of ethyl acetate. After centrifugation and evaporation, the organic residue is washed with hexane and the nitrofurans are hydrolyzed to 5-nitrofuraldehyde in aqueous acid at 70°C. The hydrolysis product is extracted with benzene and measured by gas-liquid chromatography with electron capture detection. Recoveries of nitrofurazone and furazolidone from fortified poultry and swine tissues at the levels of 0.5 and 0.1 ppm are 75 and 65%, respectively. This procedure can be used to detect the total nitrofuran content of as little as 10 ppb muscle tissues and milk, 100 ppb liver, and 50 ppb fat with no interference from related veterinary nitrodrugs.
The constituents of strawberry and raspberry have been studied in order to regulate the fruit content of jams made from these fruits. Four constituents, potassium, insoluble solids, amino acids, and phosphorus, were examined to ascertain the variation, means, and minimum acceptable values. From data taken after about 1950 from these laboratories and from the literature, the variation of the first 3 constituents was less than 30% and acceptable, while that of phosphorus was too large and rejected. Strawberry and raspberry fruit samples of known constituent content were processed into jams and the amount of fruit in jam was estimated by using the constituent values. There was little or no difference between the per cent fruit in jams found by using potassium and insoluble solids and the true values determined by weighing. The percentage of fruit using total amino acid values was unreliable and could not be used. Minimum and mean values determined for strawberry jam containing 52% fruit are, for potassium, 45 and 77 mg/100 g and, for insoluble solids, 0.49 and 0.87 g/100 g.
The common tetracyclines (TCs) which are used in agriculture, tetracycline, oxytetracycline, and chlortetracycline, are analyzed in animal tissues by using chemical-physical methods. Tissue from chicken, beef, pork, or fish is blended in aqueous HC1 and centrifuged. The supernate is adsorbed on an Amberlite X AD-2 column, the column is washed with water, and the TCs are eluted with methanol. For levels of TCs greater than 0.5 ppm in tissues and milk, the concentrated residue is spotted on a thin layer plate coated with kiesclguhr. The amount of TCs present on the developed plate is estimated by comparison of the fluorescence with standards spotted concurrently. Recovery of all 3 TCs from samples fortified at levels of 0.5-2 ppm is 45-80%. For levels less than 0.5 ppm, the residue from the Amberlite column is dissolved in pH 9 aqueous solution containing calcium ions and barbital, TCs are extracted into chloroformethanol, and the concentration is estimated on thin layer plates. Recoveries of TCs from various tissues at levels of 0.1–0.5 ppm are 10–35%.
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